A potential hazard to many field based weapon systems is the threat of gunfire and shrapnel or metal fragments thereof. The safety of the soldiers and the survivability of the system is based on the ability of the weapons of the system to absorb these fragments without deflagrating or detonating of the propellant. In particular, missile systems that are based in hostile territory are prime candidates for targeting of bullets and mortar, and realistically, a certain percentage of any deployed missile system will, at one time or another, be the subject of a hostile attack involving gunfire, or artillery. For this reason, it is extremely important to know what kind and how much metal fragments these missiles can absorb before failure of the propellant system.
A major contributing factor to the deflagration of solid propellant relates to the heat transfer between a hot fragment and the propellant. In other words, the propellant is ignited by the hot fragment.
In a "real world" scenario, the hot fragment is shot and then imbedded into the propellant. As this happens, three things can happen: 1. the propellant does not react to the fragment; 2. the fragment causes the propellant to detonate immediately; or 3. the fragment smolders in the propellant, gives off exhaust gasses, builds up a critical pressure, and finally deflagrates or detonates.
The testing of propellant to determine its reaction to a hot metal fragment has been achieved by crude spall testing. The subject of spall testing therefore is not new, and there have been different machines designed for this purpose.
These machines all consist of manually heating up a metal fragment and then dropping it onto a small piece of propellant that is subjected only to atmospheric pressure. The results are observed by eye and the data recorded by hand. A typical prior art spall tester is shown in FIG. 1. Note the crudity of the system, and the fact that the propellant is not confined in any way.
The method used with the above prior art tester has many flaws that raises questions concerning the accuracy of the results. Most importantly, the tester does not accurately reproduce the conditions in which a real propellant sample would be affected by a spall. The important concept to remember is that progressive propellant burn rate is related to the pressure that it is burning under. Some of the most advanced propellants used today burn only slowly, if at all, when exposed to atmospheric pressure. Only when the propellant has built up pressure does it burn with its high energy yield. It is for this reason that the method described above is inadequate for the accurate prediction of propellant reaction to hot fragments. The heated spall is introduced to the propellant in the atmosphere and not confined. This means that the propellant and spall are introduced and maintained at atmospheric pressure, even after the spall has started smoldering. This open condition prevents any pressure buildup and will, in many cases, cause the propellant to fail to ignite. The zero pressure buildup retards the burning of the propellant, and does not realistically simulate the action of a real heated spall in an actual missile case. This inadequacy is a large source of error.
There are other disadvantages of the method. A difference of only a few degrees in the temperature of the fragment can mean the difference between ignition or non ignition. Uniform and exact temperature repeatability are therefore very important in order to get good, accurate test data. In the existing methods, the spalls, small ball bearings, are heated individually in a furnace, and dropped one at a time onto the propellant. Since the balls are heated individually, exact and repeatable temperatures are difficult to obtain. This inconsistency surely adds another element of error to the results. The method is also very time consuming.
Due to the reason stated above, it is an object of the invention to provide a new technique and mechanism that will overcome the disadvantages of the present system as well as add many new advantages.
Another object of this invention is to provide a hot spall tester which will accurately simulate the heat transfer conditions in which a missile's propellant is contacted by a hot spall and when it is ignited under confined pressure.
Still a further object of this invention is to provide a hot spall tester which can also be used to test propellant open to the atmosphere.